Heretofore, for capturing a radiographic image of a breast of a subject using a radiographic image capturing apparatus, it has been customary to place the breast on a support table, displace a compression plate toward the support table to compress the breast, and thereafter, irradiate the breast with radiation emitted from a radiation source. Then, the radiation that has passed through the breast is converted into image data with a radiation detector.
In the above sequence, it is desirable to accurately grasp the thickness of the breast in the compressed state. In Japanese Laid-Open Patent Publication No. 6-261896, Japanese Laid-Open Patent Publication No. 2004-208752, and Japanese Laid-Open Patent Publication No. 2009-22536, it is disclosed that a position detecting sensor is provided on a proximal end portion of the compression plate, which is spaced from the chest wall of the subject, and the vertical position of the compression plate is detected by the position detecting sensor in order to measure the distance between the compression plate and the support table, i.e., to measure the thickness of the compressed breast.